Conventional planar light sources include light guiding panel-equipped light emitting diodes (hereinafter abbreviated as LEDs) and organic light emitting diodes (hereinafter also referred to as organic electroluminescence elements, organic EL elements, or OLEDs).
Light guiding panel-equipped LED light sources have rapidly come into use as general lights and, for example, from around 2008, as major components for smart devices (such as smartphones and tablets), which gain widespread use. Principal applications are backlights of main displays (such as liquid crystal displays (LCDs)). Other applications include increasing cases where a light guiding panel-equipped LED light source is incorporated as a backlight for common function key buttons arranged at the lower part of a smart device or any other device or as a backlight for a logo on the backside.
In some cases, for example, three marks “home” (indicated by a square or other mark), “return” (indicated by an arrow mark or other mark), and “search” (indicated by a magnifier mark or other mark) are provided on common function key buttons, respectively.
In order to have improved visibility, such a common function key button includes a light guiding panel; a deflection pattern having dot shapes that are previously formed in the light guiding panel depending on the pattern of the mark to be displayed; and an LED light source for applying light to the side end face of the light guiding panel.
Specifically, a known method includes printing a pattern (for the mark to be displayed) on a surface cover glass and placing a light guide panel LED under the cover glass so that light can be emitted from the LED in response to necessary situations, then transmitted through the light guiding panel (film), and then extracted to the display side through a diffusion member having dot shapes printed at the patterned part.
For example, a structure is disclosed in which light emitted from an LED light source is incident on the side end face of a light guiding panel, and the incident light is totally reflected to the front face of the light guiding panel by the deflective reflection surface of the deflection pattern and then output in a certain pattern from the front face of the light guiding panel, so that the emitted light appears in the pattern when the light guiding panel is viewed from the front side (see, for example, Patent Literature 1).
Unfortunately, the problems described below will occur when a backlight based on an LED light guide system is to be installed in a smart device. A first problem is that a thinner light guiding panel (e.g., film base material) is necessary because the smart device has a narrow installation space and a significant limitation on the thickness or size of the backlight to be installed. However, a thinner light guiding panel as a display member can reduce the luminous efficiency of LED light sources.
A second problem is that since light is guided from the side of an icon display part including a plurality of common function key buttons, the emission luminance distribution can be uneven depending on the pattern or shape of each common function key button. As a countermeasure against the uneven emission luminance distribution, the number of arranged LED light sources should be increased. However, this method can lead to an increase in cost and power consumption.
In view of the above problems, techniques for forming planar emission patterns using organic EL elements have been increasingly studied as an alternative to the light guide systems using LEDs. Organic EL elements are thin film-type, completely solid elements capable of emitting light at a low voltage of several to several tens V and have many superior properties such as low power consumption, high luminance, high luminous efficiency, emission uniformity, slimness, and light weight. In recent years, therefore, organic EL elements have been attracting attention as surface light emitters for various display backlights, display boards such as signboards and emergency lights, and illumination light sources.
Such organic EL elements have a structure in which organic functional layers including a light-emitting layer made of an organic material are stacked between two electrodes. In such elements, light is emitted from the light-emitting layer, transmitted through the electrode, and extracted to the outside. Therefore, at least one of the two electrodes is a transparent electrode, and the emitted light is extracted from the transparent electrode side. Organic EL elements can also produce high luminance at low electric power and also have superior properties in terms of visibility, response speed, life, and power consumption.
Various methods can be used to define the light-emitting area on the substrate of organic EL elements. Examples of such methods include a method of defining the light-emitting area by the shape of electrodes sandwiching a group of organic functional layers; a method of defining the light-emitting area by the shape of an insulating material formed on the electrode; a method of defining the light-emitting area by the area at which a hole or electron injection layer is deposited; a method of defining the light-emitting area by the area at which a light-emitting layer is deposited; and a method of defining the light-emitting area by carefully forming the area at which an intermediate connector for connecting light-emitting units is deposited, in the case of what is called a tandem element having a plurality of light-emitting units.
Methods for defining the shape of the light-emitting area by each of these methods include a method of defining the area shape by the shape of a mask during vapor deposition; a method of defining the area shape by physically deleting the organic layer and the electrode after the deposition; a method of defining the area shape by chemically altering the organic layer and the electrode; a photolithographic method; and a method of defining the area shape by damaging the organic layer by applying electron beams or electromagnetic waves to the organic layer.
In particular, there is known a method of patterning a light-emitting area by applying electron beams or electromagnetic waves such as ultraviolet rays to a group of organic functional layers to damage a light-emitting layer and other organic functional layers. This method attracts attention because when this method is performed using a mask, complicated shapes can be easily formed, which would otherwise be difficult to achieve by conventional techniques in view of manufacturing cost or complicated manufacturing process.
For example, there is disclosed a method of patterning a light-emitting area by applying electron beams or ultraviolet rays to a certain region so that the organic material constituting a group of organic functional layers is degraded (deactivated) in the region (see, for example, Patent Literature 2). There is also disclosed a similar method of patterning a light-emitting area by damaging the light-emitting layer of an organic EL element by applying ultraviolet rays (see, for example, Patent Literature 3).
There is also proposed an organic light-emitting element having a specific light-emitting pattern that is formed by applying ultraviolet light to at least one organic functional layer or constituent electrode layer through a photomask in the process of manufacturing an organic EL element so that the function of a predetermined pattern region is altered (see, for example, Patent Literature 4).
Unfortunately, the proposed methods have the problems described below, when used in the process of forming an icon or a logo pattern in an organic electroluminescence panel (hereinafter referred to as an organic EL panel) by applying electron beams or ultraviolet rays.
Specifically, a light-emitting part and a non-light-emitting part for a display pattern should be formed so as to achieve an emission luminance ratio of the former to the latter of about 200:1. In order to meet such conditions, the time of irradiation with ultraviolet rays or the like during the patterning should be long, which requires the ultraviolet irradiation system to have a high power and increases the size of the facility and the lead term during the manufacture, so that the economic burden increases.
Thus, there has been a demand for the development of a light-emitting panel that allows electric power to be supplied only to the light-emitting part with no need to guide light to unnecessary parts in a display method based on an LED light guide system, and also has low power consumption and improved display uniformity. There has also been a demand for a light emitting panel-forming method that has a short lead time for a patterning step using ultraviolet rays in the process of forming a display pattern in an organic EL panel, and also has low facility load and high cost-effectiveness.